Flashback shield



Jan. 20, 1959 s. M. SEGAL FLASHBACK SHIELD Filed Jan. 31, 1957 anZe M56 aZ BY I N VEN TOR.

FLASHEACK SHIELD Stanley M. Segal, Springfield, Va.

Application January 31, W57, Serial No. 637,582

1 claim. (or. 313-36) (Granted under Title 35, U. 5. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to a shield and more particularly to an electrically conductive flashback shield for protecting the water-cooled head of high intensity carbon arc lamps.

In conventional practice water-cooled jaws, which deliver current to and cool the positive carbon electrode held by the jaws in high inten3ity arc lamps, are subject to instant and costly damage. the arc flashes back to the jaws due to irregularities in arc operation. The water-cooled high intensity carbon arc operates with an intensely hot crater. The crater temperature may exceed 10,060 degrees Kelvin, and is removed only a short distance from the water-cooled head, about three-eighths of an inch in). Whenever the carbon arc feed mechanism, carbonor any of several other are parameters function improperly, there is a strong likelihood of the arc flashing to the watercooled head instead of the crater. This flashback often punctures holes in the water-cooled head causing the water to spurt out. Merely placing a protective cover against the head does not prevent the damage.

Present methods for protecting the water-cooled head from flashback damage include:

(a) Operation of the arc with a large protrusion of the positive electrode and reduced power. This process materially reduces the eifectiveness and advantages of water-cooling.

([1) Fabrication of water heads with heavy walls and small channels for conducting water. This expedient is more costly, less effective functionally, and only partially effective from the standpoint of protection.

Use of insulating shields. This expedient is only partially protective and is almost impossible to use when very short protrusions of the positive carbon electrode are specified in a particular design.

(d) Fabrication of air jets to blow away ionized paths conducive to flashbacks. This expedient is very costly and only partially protective.

The principles of operation and structure of the improved device herein disclosed difler materially from present practices. Essentially, the structure embodies a thin, replaceable, electrically conducting metal sheet which is mounted on the positive electrode support structure to place it between the water-cooled jaws and negative electrode with an opening in the shield to allow the positive electrode to project through without contacting it. The shield is electrically connected to the current input terminals of the jaws and is at the same potential as the positive carbon electrode and acts as a screen to stop any electrons directed toward the water cooled jaws which will not impinge on the positive electrode. Theoretically, with the shield at the same potential as the positive carbon electrode, which will also be the potential on the water-cooled head since the water-cooled jaws contact and hold the positive electrode, there should be This damage occurs when asrsass no arcing or electrical energy flow between the shield and the water-cooled head. With the shield so arranged and electrically connected, if any flashbacks do occur from the negative electrode to points other than the positive carbon electrode, the flashback will be directed around the Water-cooled head to the shield rather than to the water-cooled head, and thus prevent any puncturing of .he water-cooled head.

The principle and structure of the instant device permits reducing the cost of water-cooled heads, welding rather than casting the head, larger volume of water for better cooling due to the thinner walls of the watercooled head and elimination of the need for compressors or air ducts for cooling purposes and preventing flashbacks.

It is therefore the principal object of the present invention to provide a protective structure which will prevent puncturing by flashback arcing of the water-cooled jaws of high intensity carbon arc lamps.

It is a further object of the present invention to provide an electrically conducting shield for the water-v cooled jaws of high intensity carbon arc lamps to direct flashback arcing around the water-cooled head to prevent. puncturing the water-cooled head.

It is a further object of the present invention to provide a protective structure for water-cooled jaws of high intensity carbon arc lamps employing an electrically conductive shield at the same potential as the water-cooled jaws to direct flashback arcing around the water-cooled head and prevent puncturing thereof.

These and other objects will be evident as the description of the invention proceeds wherein- Fig. l is a plan view of the flashback shield and watercooled head assembly; and

Fig. 2 is a perspective view of the assembly shown in Fig. 1 with the flashback shield removed from the watercooled head.

Reference is now made to Fig. 2 wherein the watercooled head, including an upper chamber l and lower chamber 2, is secured in any convenient manner to a support 3 which may be metal or insulating material. The support 3 is in turn supported in a structure employing carbon electrodes, such as a carbon arc lamp housing. The chambers l and 2 are held together by springs 4 secured in a suitable manner to the ends of the chambers. If the support 3 is metal, an insulating member 5 is used to electrically insulate the chahbers l, 2 from the support 3. The chambers l, 2 may be con toured at their meeting faces to receive carbon electrodes,

such as the rectangular electrode I19 shown, or other,

The lower chamber 2 is provided with guides shapes. or flanges 7 to retain the upper chamber 1 in position against the support 3 or insulating member 5, if used. Cooling water is moved to and from the upper and lower chambers l and 2, respectively, through copper tubes t5 which are secured in water-tight and electrically conductive relation to the upper and lower chambers l. and 2,

respectively. In the embodiment shown in Figs. 1 and 2, each of the chambers 1 and 2 has a copper tube connected to each end of each chamber. Other arrangements for circulating cooling water and simultaneously conducting electrical energy to the upper and lower chambers, 1 and 2, may be used, or the cooling and electrical energy connections may be separate without altering the inventive concept. Further, coolants other than water, in liquid or gaseous form, may be used and circulated at high or low velocity depending on the circumstances of the design involved. The simultaneous connections of cooling water and electrical energy are accomplished by electrically conductive T-connectors, each of which has a tubular portion 8 and lug 3. A short length of copper tubing 9 is connected by means of the T-connectors to each of the copper tubes 6. The short lengths of copper tubing are each provided with a coupling member 10 to facilitate connection to a short length of flexible hose 11 which may be rubber or a plastic material. The flexible hoses 11 on each side of the chambers .1 and 2 are connected to a common pipe 12 through a Y-connection 13. Electrical energy is conducted to the chambers 1 and 2, which serve as jaws to hold the positive electrode 1% by connecting a source of electrical energy, not shown, to one of the lugs or electrical terminals 8 on one of the T-connectors at each end of the chambers 1 and 2. The electrical energy is conducted to the other T-connector connected to one of the chambers 1 or 2 on each end thereof through flexible conductors 1 connected to the lugs or electrical terminals 8' by nut and bolt means 15 as illustrated or by any other convenient means.

The flashback shield 16 is retained in position in front of the chambers 1 and Z to prevent puncturing as previously discussed, by securin the legs 1.7 to the T- connectors associated with chamber 2 by the nut and bolt means 15, which also secures the flexible conductor id to the lug or terminal 8 on these T-connectors. Thus, the flashback shield is at the same potential as the jaws and positive electrode 19, and conducts any flashback arcs which may occur, harmlessly around the jaws or chambers 1 and 2. An opening 18 in the flashback shield it) of a configuration corresponding to that of the positive electrode 19 which may be other than rectangular but of greater dimensions, permits the positive electrode to project through the flashback shield 16 the desired distance depending upon the particular design employed. The flashback shield 16 acts as a screen to stop any electron flow originating from the negative electrode and missing the positive electrode and to prevent that electron flow, or a part of it, from impinging on the water cooled chambers 1 and 2. It is obvious that the flashback shield 16 may be secured in fixed position without supporting it by bolting to the lugs 8' but in such other arrangements the flashback shield 16 must be electrically connected to the source which energizes the positive electrode 19 in accordance with the principles and teach ings of the instant invention. The flashback shield 16 may be of copper or other suitable electrically conducting sheet material, preferably of larger face area than silhouette of the head to be shielded. Although a heavier stock could be used, sheet stock provi es better results through less heat retention and minimization of the distance between the arc crater and the head coolant.

Having thus described my invention, what l claim as new and wish to secure by Letters Patent is:

In a carbon electrode device including a source of electrical energ, positive and negative electrodes, 21 lluid-cooled head supporting the positive electrode with the electrode protruding from the forward wall of the head, tube means for conducting circulating cooling fiuid and electrical energy to the fluidcooled head and the positive electrode, terminal means attached to the tube means for the introduction of electrical energy from the source and support means for the fluid-cooled head, the improvement comprising a relatively planar shield lo cated between the negative electrode and the fluid-cooled head proximate and substantially parallel to but spaced from the forward wall or" the head, the shield being of electrically conducting sheet material having an opening of the same configuration but slightly larger than the positive electrode and disposed relative to the positive electrode with that electrode extending through but spaced from the shield, the shield being dimensioned to extend beyond the bounding edges of the head and having connecting means connected to the terminal means for supporting the shield on the head and for the introduction of electrical energy to the shield in parallel with the positive electrode whereby electrical energy flowing from said negative electrode toward the positive electrode will impinge only on the positive electrode or the shield.

tic

References (F tted in the file of this patent UNlTED STATES PATENTS 2,107,148 Gretener Feb. 1, 1938 2,454,957 Zimmerman Nov. 30, 1948 2,495,970 Huff Jan. 31, 1950 2,651,736 Ashcraft Sept. 8, 1953 2,653,267 Mclntosh Sept. 22, 1953 

